Effect of PEO chain length on Triton-Assisted TMAH etching of Si(111) pillars

This work investigates the influence of non-ionic surfactants Triton X-100 and Triton X-405 on the anisotropic wet etching of (111)-oriented silicon wafer using 25 wt% tetramethylammonium hydroxide (TMAH). Circular pillars with (111) top and bottom surface were fabricated using dry etching and subsequently etched in surfactant-added-TMAH solutions. The results reveal that Triton X-100, with a shorter polyethylene oxide (PEO) chain, induces a stronger reduction in the lateral etch-rate due to higher surface adsorption on pillar sidewalls, while Triton X-405, with a longer PEO chain, results in smoother sidewalls attributed to improved hydrogen bubble removal.Both surfactants promote the formation of high aspect ratio structures, and their adsorption behavior was found to strongly affect the etch anisotropy, undercut, and final profile of the etched pillars. These findings provide insight into the role of surfactant chemistry in tailoring etch profiles for advanced silicon microfabrication applications.